Filter Structure for Removing Contaminants from Stream of Fluid

ABSTRACT

Various methods and apparatus are disclosed that relate to one or more aspects of a filter structure that may remove contaminants from a stream of fluid. In various aspects the filter structure includes a front portion having a first orientation and a rear portion having a second orientation unique from the first orientation.

CROSS-REFERENCE TO RELATED DOCUMENTS

This application (under 35 U.S.C. §119(e)) claims the benefit ofcurrently pending Provisional Patent Application Ser. No. 61/388,971,filed Oct. 1, 2010 and entitled “Filter Structure for RemovingContaminants from Stream of Fluid.”

TECHNICAL FIELD

The present invention is directed generally to aspects of a filterstructure. More particularly, various inventive methods and apparatusdisclosed herein relate to one or more aspects of a filter structure forremoving one or more contaminants from a stream of fluid such as, forexample, removing contaminants from a stream of air supplied to gasturbines or other smooth intake flow machinery.

BACKGROUND

Filters are generally used to remove one or more contaminants from astream of fluid, including gas and liquid. For example, a bank offilters may be provided in a gas filtering system upstream of a gasturbine in order to remove contaminants from a stream of fluid beingsupplied to the gas turbine. Over a period of time the filters becomeloaded with contaminants that have been removed from the stream of fluidby the filters. When the contaminant buildup on the upstream side of thefilters causes the fluid flow through the filters to be restricted by apredetermined amount, the filters are typically replaced or cleaned.

Some gas filtering systems may utilize self cleaning of the filters toperiodically remove contaminants from the filters. Such self cleaningsystems may utilize pulse back cleaning to periodically discharge burstsof air into the filters in an opposite direction from the typical flowof fluid, thereby causing reversal of the fluid flow moving through thefilters and a sudden change in pressure causing the removal ofcontaminants accumulated on the upstream side of the filters. Thedislodged contaminants may be drawn into a secondary cleaning aircircuit on the upstream side of the filters to minimize re-entrainmentof the dislodged contaminants back into the filters. The pulse backcleaning decreases the amount of contaminants on the upstream side ofthe filters and resultantly reduces the amount of restriction of thefluid flow. The pulse back cleaning accordingly reconditions the filtersfor continued, substantially uninterrupted service and increases theinterval for servicing the filters. One such gas filtering system thatutilizes a bank of filters and pulse back cleaning is the ASC III IntakeFilter System available from AAF International of Louisville, Ky.

SUMMARY

The present disclosure is directed to inventive methods and apparatusfor aspects of a filter structure, and, more specifically, one or moreaspects of a filter structure for removing one or more contaminants froma stream of fluid. For example, some aspects of the present disclosureare directed to a filter structure for removing contaminants from astream of air supplied to gas turbines or other smooth intake flowmachinery and other aspects are directed to a gas filtering systemcontaining a plurality of filter structures.

Generally, in one aspect, a filter structure for removing contaminantsfrom a stream of fluid is provided. The filter structure includes afront filter portion and a rear filter portion. The front filter portionhas a front frame supporting a front first filter and a front secondfilter. The front first filter and the front second filter are insubstantially parallel spaced relation to one another and define asubstantially parallel front clean air passageway therebetween. Thefront frame includes a front end plate extending between the front firstfilter and the front second filter proximal a first filter first end ofthe front first filter and a second filter first end of the front secondfilter. The rear filter portion has a rear frame supporting a rear firstfilter and a rear second filter. The rear first filter extends fromadjacent a first filter second end of the front first filter and therear second filter extends from adjacent a second filter second end ofthe front second filter. The rear first filter and the rear secondfilter are in diverging spaced relation with one another as they extendfrom adjacent respective of the front first filter and the front secondfilter and define a substantially diverging rear clean air passagewaytherebetween. The rear clean air passageway and the front clean airpassageway are in flow communication with one another. The rear frameincludes a rear end plate having a rear end plate opening in flowcommunication with the rear clean air passageway. The rear end plate isconfigured for interfacing with a clean air intake opening.

In some embodiments the front frame and the rear frame contain at leastsome unified structure. In some versions of those embodiments the frontfirst filter and the rear first filter contain at least some unifiedstructure.

In some embodiments the front filter portion and the rear filter portionare separable from one another. In some versions of those embodimentsthe front frame portion includes a second front end plate extendingbetween the first filter second end and the second filter second end.The second front end plate may include a second front end plate openingtherein in flow communication with the front clean air passageway andmay be configured to removably engage the rear frame.

In some embodiments the front frame includes a front upper framestructure and a front lower frame structure sandwiching the front firstfilter and the front second filter.

In some embodiments the front first filter and the front second filtershare a substantially similar first material configuration and the rearfirst filter and the rear second filter share a substantially similarsecond material configuration distinct from the first materialconfiguration. In some versions of those embodiments the first materialconfiguration has a first average pleat density and the second materialconfiguration has a second average pleat density. In certain embodimentsthe second average pleat density may optionally be at least fifteenpercent more dense than the first average pleat density.

In some embodiments the front first filter and the front second filtershare a substantially similar first length and the rear first filter andthe rear second filter share a substantially similar second lengthdistinct from the first length. In some versions of those embodimentsthe first length is at least fifteen percent greater than the secondlength.

Generally, in another aspect, a filter structure for removingcontaminants from a stream of fluid is provided and includes a generallyrectangular front filter portion and a generally trapezoidal rear filterportion. The front filter portion includes front frame structuresupporting a first front filter and a second front filter insubstantially parallel spaced relation to one another. The front framestructure, the first front filter, and the second front filtersubstantially surround a front clean air passageway. The rear filterportion includes rear frame structure supporting a first rear filter anda second rear filter in substantially divergent spaced relation with oneanother. A less spaced end of the first rear filter and the second rearfilter is proximal the front filter portion and a more spaced end of thefirst rear filter and the second rear filter is distal the front filterportion. The rear frame structure, the first rear filter, and the secondrear filter substantially surround a rear clean air passageway. The rearclean air passageway is in communication with the front clean airpassageway and in communication with a filter structure outlet betweenthe first rear filter and the second rear filter proximal the morespaced end of the first rear filter and the second rear filter.

In some embodiments the front first filter and the rear first filtercontain at least some unified structure. In some versions of thoseembodiments the front frame and the rear frame contain at least someunified structure.

In some embodiments the front first filter and the front second filtershare a substantially similar first material configuration and the rearfirst filter and the rear second filter share a substantially similarsecond material configuration distinct from the first materialconfiguration. In some versions of those embodiments the first materialconfiguration has a first average pleat density and the second materialconfiguration has a second average pleat density. In certain embodimentsthe second average pleat density may optionally be at least ten percentmore dense than the first average pleat density. In other certainembodiments the second average pleat density may optionally be at leasttwenty percent more dense than the first average pleat density. In someversions of those embodiments the first material configuration has afirst grade and the second material configuration has a second gradedistinct from the first grade. In some versions of those embodiments thefront filter portion and the rear filter portion are separable from oneanother.

Generally, in another aspect a filter structure for removingcontaminants from a stream of fluid includes a front filter portion anda rear filter portion. The front filter portion defines a front cleanair passageway therein and has a first front filter and a second frontfilter flanking the front clean air passageway. The first front filterand the second front filter are at a first orientation relative to oneanother. The rear filter portion is coupled to the front filter portionand defines a rear clean air passageway therein. The rear clean airpassageway is in flow communication with the front clean air passagewayand the rear filter portion has a first rear filter and a second rearfilter flanking the rear clean air passageway. The first rear filter andthe second rear filter are at a second orientation relative to oneanother that is distinct from the first orientation. The front firstfilter and the front second filter share a substantially similar firstaverage pleat density and the rear first filter and the rear secondfilter share a substantially similar second average pleat densitydistinct from the first average pleat density.

In some embodiments the second average pleat density is at least fifteenpercent more dense than the first average pleat density. In someembodiments the second average pleat density is at least twenty-fivepercent more dense than the first average pleat density. In someembodiments the front first filter portion and the rear first filterportion contain at least some unified structure.

In some embodiments the first orientation is a substantially parallelorientation.

In some embodiments the second orientation is a diverging orientationand the first rear filter and the second rear filter are more proximalone another adjacent the coupling between the front filter portion andthe second filter portion.

Generally, in another aspect a fluid filtering system is provided. Thefluid filtering system includes a plurality of filter structuresinterposed between an unfiltered fluid intake area and a filtered fluidoutput area. The filter structures have an air passageway thereinflanked by a first side filter portion and a second side filter portion.The air passageway is in communication with the filtered fluid outputarea. The first side filter portion and the second side filter portionallow communication of fluid therethrough both into and out of the airpassageway. The first side filter portion and the second side filterportion have a substantially parallel orientation with respect to oneanother along a first length and have a substantially divergingorientation with respect to one another along a second length. The firstlength is more distal the filtered fluid output area than the secondlength. Along the second length the first side filter portion and thesecond side filter portion become more divergent as they become moreproximal the filtered fluid output area.

In some embodiments the first side filter portion includes a frontfilter portion along the first length that is non-unified with a rearfilter portion along the second length.

In some embodiments the first filter and the second filter share asubstantially similar first average pleat density along at least aportion of the first length and the first filter and the second filtershare a substantially similar second average pleat density along atleast a portion of the second length. In certain embodiments the secondaverage pleat density is at least twenty percent more dense than thefirst average pleat density.

In some embodiments the filter structures are separable into a frontfilter structure that includes the first length and a rear filterstructure that includes the second length.

In some embodiments the fluid filtering system includes at least onesecondary air circuit opening provided between two side by side filterstructures.

It should be appreciated that all combinations of the foregoing conceptsand additional concepts discussed in greater detail below (provided suchconcepts are not mutually inconsistent) are contemplated as being partof the inventive subject matter disclosed herein. In particular, allcombinations of claimed subject matter appearing at the end of thisdisclosure are contemplated as being part of the inventive subjectmatter disclosed herein. It should also be appreciated that terminologyexplicitly employed herein that also may appear in any disclosureincorporated by reference should be accorded a meaning most consistentwith the particular concepts disclosed herein.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, like reference characters generally refer to the sameparts throughout the different views. Also, the drawings are notnecessarily to scale, emphasis instead generally being placed uponillustrating the principles of the invention.

FIG. 1 illustrates an upper rear first side perspective view of a firstembodiment of a filter structure.

FIG. 2 illustrates an upper rear first side perspective view of thefirst embodiment of a filter structure of FIG. 1; a rear filter portionof the filter structure is shown exploded away from a front filterportion of the filter structure.

FIG. 3 illustrates an upper front first side perspective view of thefirst embodiment of a filter structure of FIG. 1; the rear filterportion of the filter structure is shown exploded away from the frontfilter portion of the filter structure.

FIG. 4A illustrates a rear plan view of the first embodiment of a filterstructure of FIG. 1.

FIG. 4B illustrates a front plan view of the first embodiment of afilter structure of FIG. 1.

FIG. 5 illustrates a top view of the first embodiment of a filterstructure of FIG. 1.

FIG. 6 illustrates a first side view of the first embodiment of a filterstructure of FIG. 1.

FIG. 7 illustrates an exploded rear upper perspective view of the frontportion of the first embodiment of a filter structure of FIG. 1.

FIG. 8 illustrates an exploded rear upper perspective view of the rearportion of the first embodiment of a filter structure of FIG. 1.

FIG. 9 illustrates an upper rear perspective view of the firstembodiment of the filter structure of FIG. 1; a guide structure is alsoshown exploded away from track structure of the filter structure.

FIG. 10 illustrates an upper rear first side perspective view of asecond embodiment of a filter structure.

FIG. 11 illustrates an upper rear first side perspective view of thesecond embodiment of a filter structure of FIG. 10; a rear filterportion of the filter structure is shown exploded away from a frontfilter portion of the filter structure.

FIG. 12A illustrates a rear plan view of the second embodiment of afilter structure of FIG. 10.

FIG. 12B illustrates a front plan view of the second embodiment of afilter structure of FIG. 10.

FIG. 13 illustrates an upper rear perspective view of the secondembodiment of the filter structure of FIG. 10; a guide structure is alsoshown exploded away from track structure of the filter structure.

FIG. 14 illustrates an upper rear perspective view of aspects of a gasfiltering system that incorporates a plurality of the second embodimentof the second embodiment of the filter structures of FIG. 2; theplurality of filter structures are depicted exploded away from aplurality of guide structures extending from vertical secondary airducts; the secondary air ducts form clean air intakes therebetween.

FIG. 15 illustrates an upper rear perspective view of the aspects of agas filtering system of FIG. 14; each of the filter structures isdepicted slidably received on one of the guide structures and is incommunication with one of the clean air passageways; panels of an airfiltering housing are also depicted exploded away from one another.

FIG. 16 illustrates an upper rear perspective view of the aspects of agas filtering system of FIG. 14 and illustrates the panels of an airfiltering housing of FIG. 15; the panels of an air filtering housing aredepicted unexploded and in phantom.

FIG. 17 illustrates a top view of the aspects of a gas filtering systemof FIG. 14 and illustrates the panels of an air filtering housing ofFIG. 15; the panels of an air filtering housing are depicted in phantom.

DETAILED DESCRIPTION

In the following detailed description, for purposes of explanation andnot limitation, representative embodiments disclosing specific detailsare set forth in order to provide a thorough understanding of theclaimed invention. However, it will be apparent to one having ordinaryskill in the art having had the benefit of the present disclosure thatother embodiments according to the present teachings that depart fromthe specific details disclosed herein remain within the scope of theappended claims. Moreover, descriptions of well-known apparatuses andmethods may be omitted so as to not obscure the description of therepresentative embodiments. Such methods and apparatuses are clearlywithin the scope of the claimed invention. For example, the aspects of afluid filtering system disclosed herein are described in conjunctionwith a plurality of filter structures that are arranged in a specificfashion and that interface with other structural components of the fluidfiltering system in a specific fashion. However, one or more aspects ofa fluid filtering system described herein may be implemented with filterstructures arranged in alternative configurations and/or with filterstructures that interface with other structural components of the fluidfiltering system in alternative ways. Also, for example, as described inadditional detail herein, filter structures disclosed herein may vary inone or more respects from those specifically depicted herein.Implementation of these and other variations is contemplated withoutdeviating from the scope or spirit of the claimed invention.

In FIG. 1 through FIG. 9 various aspects of a first filter structure 100are depicted. In FIG. 10 through FIG. 13 various aspects of a secondfilter structure 200 are depicted. In FIG. 14 through FIG. 17 aplurality of the second filter structures 200 are depicted implementedin combination with other aspects of a gas filtering system.

Referring initially to FIG. 1 through FIG. 9, the first filter structure100 includes a front filter portion 101 and a rear filter portion 103.The terms front and rear are used herein for convenience in describingthe first filter structure 100 and the second filter structure 200.Generally speaking, the term front filter portion references a portionof filter structure that will be more proximal to the intake forincoming unfiltered air than the rear filter portion when the filterstructure 100 or 200 is installed in a fluid filtering system. Likewise,the term rear filter portion references a portion of filter structurethat will be more distal to the intake for incoming unfiltered air thanthe front filter portion when the filter structure 100 or 200 isinstalled in a fluid filtering system and that will be more proximal toa clean air intake opening of the fluid filtering system than the frontfilter portion. In the depicted embodiment, the front filter portion 101and the rear filter portion 103 are separable from one another asillustrated in the exploded views of FIG. 2 and FIG. 3 and as describedin more detail herein.

The front filter portion 101 includes a front first filter having afront first filter upstream face 112 and a front first filter downstreamface (not visible in the Figures) opposite the front first filterupstream face 112. The front filter portion 101 also includes a frontsecond filter having a front second filter upstream face 122 (FIG. 9)and a front second filter downstream face 126 (FIG. 2 and FIG. 7). Inthe depicted embodiment the front first filter and the front secondfilter are in substantially parallel spaced relation with respect to oneanother and may be up to about 4 degrees or more angle of inclinationfrom parallel. It is understood that the term face as used herein doesnot mandate a planar surface. Rather, a face may be non-planar such as,for example, a face formed by a plurality of filter pleats.

Only small representative sections 112 a, 122 a, and 126 a of respectivefiltering media of front first filter upstream face 112, front secondfilter upstream face 122, and front second filter downstream face 126are shown throughout FIG. 1 through FIG. 9. It should be understood thatthe entire upstream face and downstream face of the front first filterand front second filter may be constructed of filtering media. Also, itshould be understood that the particular depiction of representativesections 112 a, 122 a, and 126 a should not be regarded as limiting thetype of filtering media that may be utilized in the filtering structuresdescribed herein. In some embodiments the filtering media may be apleated media and may optionally incorporate longitudinally extendingstiffeners interspersed throughout the media to increase rigiditythereof.

Although not depicted for sake of clarity, in some embodiments permeablesupport material may be provided on the upstream and/or downstream faceof the front first filter and/or the front second filter. For example, awire mesh guard sheet may be provided against upstream face 112 and thedownstream face of the first front filter and upstream face 122 and thedownstream face 126 of the front second filter. Such a wire mesh guardmay sandwich the filters and increase the effective rigidity of thefilters.

The front first filter and the front second filter are supported by afront frame. The depicted front frame includes a front upper framestructure 142, a front lower frame structure 144, a front first endplate 132, and a front second end plate 134. The front frame supportsthe front first filter and the front second filter in parallel spacedrelation to one another. The upper frame structure 142 includes a firstlongitudinal recess on an interior facing surface thereof that receivesa top portion of the front first filter and a parallel secondlongitudinal recess on the interior facing surface that receives a topportion of the front first filter. Likewise, the lower frame structure144 includes first and second parallel longitudinal recesses (visible inFIG. 7) on an interior surface thereof that receive a lower portion ofthe front first filter and front second filter, respectively. In thedepicted embodiment the upper frame structure 142 and the lower framestructure 144 have substantially the same configuration.

The front first end plate 132 extends over first ends of the front firstfilter and the front second filter and extends between the front firstand second filters. The front first end plate 132 includes two smallopenings 132 a and 132 b, but is otherwise solid and non-permeable. Asdescribed in additional detail herein, the openings 132 a and 132 b areutilized to secure the first filter structure 100 in a filtering systemand will be substantially blocked when the first filter structure 100 isinstalled. A front first end plate spacer 133 (FIG. 4A, FIG. 7) may becoupled to the interior facing surface of first end plate 132 and willbe interposed between the front second filter downstream face 126 andthe front first filter downstream face. Accordingly, when first filterportion 101 is assembled the first ends of the front first filter andthe front second filter are interposed between the front first end platespacer 133 and a peripheral flange of the first end plate 132. The frontend plate spacer 133 includes openings 133 a and 133 b that align withopenings 132 a and 132 b. Openings 133 a and 133 b are also are utilizedto secure the first filter structure 100 in a filtering system and willbe substantially blocked when the first filter structure 100 isinstalled.

The front second end plate 136 extends over second ends of the frontfirst filter and the front second filter and extends between the frontfirst and second filters. The front second end plate 136 includes afront second end plate air passageway opening 137 formed therein. Thefront second end plate air passageway opening 137 has an interiorlyextending flange therearound. When first filter portion 101 isassembled, the second ends of the front first filter and the frontsecond filter will be interposed between the interiorly extending flangeof the front second end plate air passageway opening 137 and aperipheral flange of the second end plate 136.

The front first filter, the front second filter, the front upper framestructure 142, the front lower frame structure 144, and the front firstend plate 132 surround and define a front air passageway 102 (FIG. 2).The front second end plate air passageway opening 137 provides access tothe front air passageway 102 and provides for communication of air toand from the air passageway 102. As described in additional detailherein, air may also be communicated to or from the front air passageway102 by moving through the front first filter or the front second filter.

The rear filter portion 103 of first filter structure 100 includes arear first filter having a rear first filter upstream face 152 and arear first filter downstream face 156 (FIG. 9) opposite the rear firstfilter upstream face 152. The rear filter portion 103 also includes arear second filter having a rear second filter upstream face 162 (FIG.9) and a rear second filter downstream face 166. In the depictedembodiment the rear first filter and the rear second filter are in adiverging spaced relation with respect to one another and become moredivergent as they move become more distal the front filter portion 101.In the depicted embodiment the rear first filter and the rear secondfilter are diverging at approximately a ten degree angle with respect toone another. In alternative embodiments different diverging angularrelationships may be utilized in order to, inter alia, achieve desiredperformance characteristics.

Only small representative sections 152 a, 156 a, 162 a, and 166 a ofrespective filtering media of rear first filter upstream face 152, rearfirst filter upstream face 156, rear second filter upstream face 162,and rear second filter downstream face 166 are shown throughout FIG. 1through FIG. 9. It should be understood that the entire upstream faceand downstream face of the rear first filter and rear second filter maybe constructed of filtering media. Also, it should be understood thatthe particular depiction of representative sections 152 a, 156 a, 162 a,and 166 a should not be regarded as limiting the type of filtering mediathat may be utilized in the filtering structures described herein. Insome embodiments the filtering media may be a pleated media and mayoptionally incorporate longitudinally extending stiffeners interspersedthroughout the media to increase rigidity thereof. In some embodimentspermeable support material may be provided on the upstream and/ordownstream face of the rear first filter and/or the rear second filter.

The rear first filter and the rear second filter are supported by a rearframe. The depicted rear frame includes a rear upper frame structure182, a rear lower frame structure 184, a rear first end plate 172, and arear second end plate 176. The rear frame supports the rear first filterand the rear second filter in diverging spaced relation to one another.The upper frame structure 182 includes a first longitudinal recess on aninterior facing surface thereof that receives a top portion of the rearfirst filter and a divergent second longitudinal recess on the interiorfacing surface that receives a top portion of the rear first filter.Likewise, the lower frame structure 184 includes first and seconddiverging longitudinal recesses (visible in FIG. 8) on an interiorsurface thereof that receive a lower portion of the rear first filterand rear second filter, respectively. In the depicted embodiment upperframe structure 182 and lower frame structure 184 may have asubstantially similar configuration.

The rear first end plate 172 extends over first ends of the rear firstfilter and the rear second filter and extends between the rear first andsecond filters. The rear first end plate 172 includes a rear first endplate air passageway opening 173 formed therein. The rear first endplate air passageway opening 173 has an interiorly extending flangetherearound (FIG. 8). When rear frame portion 103 is assembled the firstends of the rear first filter and the rear second filter will beinterposed between the interiorly extending flange of the rear first endplate air passageway opening 173 and a peripheral flange of the rearfirst end plate 172. A gasket 174 is provided around the rear first endplate air passageway opening 173. The gasket 174 is positioned so thatwhen the front portion 101 and rear portion 103 are engaged with oneanother it sealingly engages the front first end plate 136 and placesthe front second end plate air passageway opening 137 and the rear firstend plate air passageway opening 173 in communication with one another.As described in more detail herein, when the filter structure 100 isinstalled the front portion 101 and the rear portion 103 maycollectively compress the gasket 174 to enhance the seal between therear first end plate 172 and the front second end plate 136. Inalternative embodiments a gasket may additionally or alternatively beprovided on the front second end plate 136.

The rear second end plate 176 extends over second ends of the rear firstfilter and the rear second filter and extends between the rear first andsecond filters. The rear second end plate 176 includes a rear second endplate air passageway opening 177 formed therein. The rear second endplate air passageway opening 177 has an interiorly extending flangetherearound. When rear filter portion 103 is assembled the second endsof the rear first filter and the rear second filter will be interposedbetween the interiorly extending flange of the rear second end plate airpassageway opening 177 and a peripheral flange of the second end plate176. A gasket 178 is provided around the rear second end plate airpassageway opening 177.

The rear first filter, the rear second filter, the rear upper framestructure 182, and the rear lower frame structure 184 surround a rearair passageway 104. The rear first end plate air passageway opening 173provides access to the rear air passageway 104 and provides forcommunication of air into and out of the rear air passageway 104. Therear first end plate air passageway opening 173 also provides forcommunication of air between the rear air passageway 104 and the frontair passageway 102 when the front portion 101 and the rear portion 103are engaged with one another. The rear second end plate air passagewayopening 177 also provides access to the rear air passageway 104 andprovides for communication of air into and out of the rear airpassageway 104. The rear second end plate air passageway opening 177also provides for communication of air between the rear air passageway104 and a clean air intake opening when the filtering structure 100 isinstalled in an air filtering system. As described in additional detailherein, air may also be communicated to or from the rear air passageway104 by moving through the rear first filter or the rear second filter.

The gasket 178 is positioned so that when the filter structure 100 isinstalled in a fluid filtering system the gasket 178 will sealinglyengage a clean air intake opening, thereby placing the clean air intakeopening in communication with the rear and front clean air passageways104 and 102. As described in more detail herein, when the filterstructure 100 is installed, the rear portion 103 and the clean airintake opening may compress the gasket 178 to enhance the seal betweenthe rear second end plate 176 and the clean air intake opening.

Referring particularly to FIG. 7, a front upper track structure 143 isdepicted that is coupled to an interior surface of front upper framestructure 142. A front lower track structure 145 is also depicted thatis coupled to an interior surface of front lower frame structure 144.Referring particularly to FIG. 8, a rear upper track structure 183 isdepicted that is coupled to an interior surface of rear upper framestructure 182. A rear lower track structure 185 is also depicted that iscoupled to an interior surface of rear lower frame structure 182. Thetrack structures 143, 183, 145, and 185 may be utilized to guide and/orsecure the filter structure 100 in a fluid filtering system.

For example, referring particularly to FIG. 9, a guide structure 190 isdepicted exploded away from the filter structure 100. The guidestructure 190 includes an upper guide structure 191 that may be slidablyreceived in front and rear upper track structure 143, 183 and alsoincludes a lower guide structure 192 that may be slidably received infront and rear lower track structure 145, 185. A transverse coupling bar193 and a coupling plate 194 are provided at a rear end of the guidestructure 190 and may be utilized to couple the guide structure 190adjacent a clean air intake opening within a fluid filtering system. Thetransverse coupling bar 193 and/or the coupling plate 194 may alsodefine a portion of a clear air intake opening. An upper fastenerreceiver 191 a and a lower fastener receiver 191 b are provided at afront end of the guide structure 190. The upper fastener receiver 191 awill align with opening 133 a in front end plate spacer 133 and opening132 a in front first end plate 132 when first filter structure 100 isslidably received on guide structure 190. Likewise, the lower fastenerreceiver 192 a will align with opening 133 b in front end plate spacer133 and opening 132 b in front first end plate 132. Fasteners may thenbe inserted through openings 132 a, 133 a, 132 b, and 133 b and receivedin respective of fastener receiver 191 a and 191 b to thereby furthersecure filter structure 100 to guide structure 190. The fasteners mayseal openings 132 a, 133 a, 132 b, and 133 b and optionally gasketwashers and/or other materials may be used in combination with thefasteners in sealing openings 132 a, 133 a, 132 b, and 133 b. When thefasteners are received in the fastener receivers 191 a and 191 b, it maycause compressive force to be applied to gasket 178 by rear second endplate 176 and other structure of fluid filtering system (e.g.,transverse coupling bar 193, or and/or structure adjacent a clean airintake opening). Moreover, it may cause compressive force to be appliedon gasket 174 by front second end plate 136 and rear first end plate172.

Optionally, when installing the filter structure 100 on the guidestructure 190, the rear filter portion 103 may first be individuallyslidably received on the guide structure 190, then the front filerportion 101 may be individually slidably received on the guide structure190. Likewise, the front filter portion 101 and the rear filter portion103 may be individually removed from the guide structure 190. Although aseparable rear filter portion 103 and front filter portion 101 aredepicted in FIG. 1 through FIG. 9 in alternative embodiments rear filterportion 103 and front filter portion 101 may be inseparable. Forexample, in some embodiments rear filter portion 103 and front filterportion 101 may be permanently coupled to one another. Also, forexample, one or more aspects of front filter portion 101 and rear filterportion 103 may be monolithically formed with one another. For example,front upper frame structure 142 and rear upper frame structure 182 maybe monolithically formed with one another.

In some embodiments of the first filter structure 100, the filter mediaof the front first filter, the front second filter, the rear firstfilter, and/or the rear second filter may comprise a synthetic media. Inversions of those embodiments the synthetic media may be Hollingsworthand Vose FA6900 NANOWEB® media. In some embodiments of the first filterstructure 100, the filter media of the front first filter, the frontsecond filter, the rear first filter, and/or the rear second filter maycontain pleats having an average depth of approximately fortymillimeters. The material may be, as an example, a composite of 60-80%by weight of melt blown polypropylene and 20-40% by weight of cellulosepaper filtration layer. The composite may act as both an efficiency anddust loading layer.

In some embodiments the front first filter media and the front secondfilter media may share a substantially similar configuration. In someembodiments the rear first filter media and the rear second filter mediamay share a substantially similar configuration. Optionally, theconfiguration of the rear first filter media and the rear second filtermedia may be distinct in at least one respect from configuration of thefront first filter media and the front second filter media.

For example, in some embodiments the rear first filter media and therear second filter media may have a substantially similar first averagepleat density and the front first filter media and the front secondfilter media may have a substantially similar second average pleatdensity that is distinct from the first average pleat density. Forexample, the rear first filter media and the rear second filter mediamay each have a pleat density of approximately thirty pleats per onehundred millimeters and the front first filter media and the frontsecond filter media may each have a pleat density of approximatelytwenty-two pleats per one hundred millimeters. In other embodiments therear first filter media and the rear second filter media may have apleat density that is less than the pleat density of the front firstfilter media and the front second filter media. Also, for example, insome embodiments the rear first filter media and the rear second filtermedia may have a substantially similar first average grade or efficiencyand the front first filter media and the front second filter media mayhave a substantially similar second average grade or efficiency that isdistinct from the first average grade. Also, for example, in someembodiments the first filter structure 100 may have a first averagepleat density over a first length thereof and a second average pleatdensity over a second length thereof. The first length may include allor portions of the front first and second filters and may optionallyinclude portions of the rear first and second filters. Likewise, thesecond length may include all or portions of the rear first and secondfilters and may optionally include portions of the front first andsecond filters. Varying the pleat density and/or the grade of the mediaalong the length of the first filter structure 100 may enable control ofdust loading to certain sections of the media. For example, varying thepleat density and/or the grade of the media along the length of thefirst filter structure 100 may ‘direct’ more airflow into the rearfilter portion 103.

When in use in a fluid filtering system, fluid to be filtered is drawnthrough the first filter structure 100 and into the air passagewaythereof (which includes the front air passageway 102 and the rear airpassageway 104). The fluid is drawn into the air passageway through thevarious filters of the first filter structure 100 and is filtered as itmoves through the various filters. The geometric profile and/or thematerial configuration of the filters of the filter structure 100 mayprovide improved air flow distribution and/or improved contaminantloading characteristics in the filters. The geometric profile and/or thematerial configuration of the filters of the filter structure 100 mayadditionally or alternatively increase the internal effectivedifferential pressure zone in at least the front filter portion 101. Thegeometric profile and/or the material configuration of the filters ofthe filter structure 100 may additionally or alternatively increaseinternal volumetric airflow in at least the front filter portion 101.The geometric profile and/or the material configuration of the filtersof the filter structure may provide for efficiency of approximatelyninety percent in some embodiments.

Upon the reaching of a certain condition in the fluid filtering system(e.g., a certain pressure being reached at one or more locations or apredetermined amount of time elapsing), one or more bursts of air may beemitted by the fluid filtering system into the filter structure 100 inan opposite direction from the typical flow of fluid to thereby causereversal of the fluid flow moving through the filters (e.g., fluid flowexiting the air passageway through the filters of the first filterstructure 100) and a sudden change in pressure. The burst(s) of airand/or change in pressure may cause the removal of contaminantsaccumulated on the upstream side of the filters. The geometric profileand/or the material configuration of the filters of the filter structure100 may provide improved reverse air flow distribution that morestrongly targets areas of the filters more likely loaded withcontaminants during normal operation. For example, the geometric profileand/or the material configuration of the filters of the filter structure100 may provide increased air distribution in the rear filter portion103. The geometric profile and/or the material configuration of thefilters of the filter structure 100 described herein may cause fasterloading of contaminants on the upstream side of the filters but may alsoreduce the number of reverse air flow pulses necessary to removecontaminants from upstream sides of the filters.

In some embodiments the following elements of the first filter structure100 may have approximately the hereinafter indicated dimensions. Therear second end plate opening 177 may be approximately 145 mm by 570 mm.The rear first end plate opening 173 may be approximately 92 mm by 570mm. The front second end plate opening 137 may be approximately 92 mm by570 mm. The front first filter and the front second filter may beapproximately 754 mm (longitudinally) by 600 mm and may be approximately42 mm thick. The rear first filter and the rear second filter may beapproximately 605 mm (longitudinally) by 450 mm and may be approximately42 mm thick.

Provided below in Table 1 is test data showing various test results foran embodiment of the first filter structure 100 utilizing the parametersof the ARAMCO 32-AMSS-008 testing method.

TABLE 1 Initial System Resistance @ 100% 0.47″ w.g. @ 6876 m³/hr RatedFlow Time to Reach Stabilized Differential   9 hrs Pressure of 2.5″ w.g.Efficiency Rating F9 Stabilised System Differential Pressure -  2.1″w.g. Phase 2 of ARAMCO Test Time Taken To Reach 10″ w.g. at  900 mins570 mg/m³ dust loading Time Taken to Pulse Clean Back from  6.5 mins 10″w.g. to within Normal Operating Range

Provided below in Table 2 is test data showing differential pressurereadings (in pascal) for an embodiment of the first filter structure 100before pulse back cleaning commenced and after one, two, and three pulsebacks. The test was conducted with a main flow set at approximately127.9 m³/min, with no secondary flow, with relative humidity atapproximately 40-50%, with a pulse manifold set at approximately 6.0 bargauge, a pulse duration of approximately 100 ms, and an inter pulseduration of approximately 30 seconds.

TABLE 2 Differential Pressure (Pa) Before Pulsing Commenced 849.3 AfterPulse 1 623.2 After Pulse 2 425.8 After Pulse 3 320.2

Analyzing the data from Table 2, it can be recognized that a 26.6%decrease in differential pressure (compared to 849.3 Pa) was achievedafter the first pulse back, a 49.9% decrease in differential pressure(compared to 849.3 Pa) was achieved after the second pulse back, and a62.3% decrease in differential pressure (compared to 849.3 Pa) wasachieved after the third pulse back.

Referring now to FIG. 10 through FIG. 13, various aspects of a secondfilter structure 200 are depicted. The second filter structure 200shares a similar configuration as the first filter structure 100, buthas a differently configured rear second end plate 276, differentlysized rear second end plate opening 277, and differently sized gasket278. Accordingly, description concerning many aspects of second filterstructure 200 is omitted herein for purpose of conciseness. However, itis understood that those aspects of second filter structure 200 havingnumbering of 2XX share a common configuration with those aspects offirst filter structure 100 having numbering of 1XX. For example, frontupper frame structure 242 has a common configuration as front upperframe structure 142. Moreover, certain aspects of second filterstructure 200 are not shown in FIG. 10 through FIG. 13, but it isunderstood that such aspects may share a similar configuration withaspects of first filter structure 100 shown in FIG. 1 through FIG. 9.For example, a front upper track structure coupled to the interiorsurface of front upper frame structure 242 is not visible in FIG. 10though FIG. 13. However, it is understood that such front upper trackstructure may share a similar configuration with the front upper trackstructure 143. In some embodiments the second end plate opening 277 mayhave dimensions of approximately 92 mm by 570 mm. In some embodimentsthe second end plate opening 277 may be sized and configured tointerface with a preexisting clean air intake opening, allowing secondfilter structure 200 to be utilized in a retrofit situation and replacepreexisting filter structures. A smaller second end plate opening 277may cause differential pressure to increase as compared to first filterstructure 100. A smaller second end plate opening 277 may also reducerated airflow as compared to first filter structure 100.

Provided below in Table 3 is test data showing various test results foran embodiment of the second filter structure 200 utilizing the ARAMCO32-AMSS-008 testing method.

TABLE 3 Initial System Resistance @ 100% 0.65″ w.g. @ 6881 m³/hr RatedFlow Time to Reach Stabilized Differential  5.5 hrs Pressure of 2.5″w.g. Efficiency Rating F9 Stabilised System Differential Pressure - 1.9″ w.g. Phase 2 of ARAMCO Test Time Taken To Reach 10″ w.g. at  800mins 570 mg/m³ dust loading Time Taken to Pulse Clean Back from   6 mins10″ w.g. to within Normal Operating Range

Provided below in Table 4 is test data showing differential pressurereadings (in pascal) for an embodiment of the second filter structure200 before pulse back cleaning commenced and after one, two, three,four, five, and six pulse backs. The test was conducted with a main flowset at approximately 127.9 m³/min, with no secondary flow, with relativehumidity at approximately 40-50%, with a pulse manifold set atapproximately 6.0 bar gauge, a pulse duration of approximately 100 ms,and an inter pulse duration of approximately 30 seconds.

TABLE 4 Differential Pressure (Pa) Before Pulsing Commenced 851.0 AfterPulse 1 765.5 After Pulse 2 657.5 After Pulse 3 551.5 After Pulse 4537.5 After Pulse 5 516.5 After Pulse 6 506.5

Analyzing the data from Table 4 it can be recognized that a 10% decreasein differential pressure (compared to 851.0 Pa) was achieved after thefirst pulse back, a 22.7% decrease in differential pressure (compared to851.0 Pa) was achieved after the second pulse back, a 35.2% decrease indifferential pressure (compared to 851.0 Pa) was achieved after thethird pulse back, a 36.8% decrease in differential pressure (compared to851.0 Pa) was achieved after the fourth pulse back, a 39.3% decrease indifferential pressure (compared to 851.0 Pa) was achieved after thefifth pulse back, and a 40.5% decrease in differential pressure(compared to 851.0 Pa) was achieved after the sixth pulse back.

Referring now to FIG. 14 through FIG. 17, a bank 1200 of the secondfilter structures 200 are depicted implemented in combination with otheraspects of a gas filtering system. Twenty of second filter structures200 are included in the bank 1200. In FIG. 14 the bank 1200 is shownexploded away from twenty guide structure 190 that are coupled to sixsecondary air ducts 195 a-f. The secondary air ducts 195 a-f form cleanair passageways therebetween. For example, a clean air passageway isformed between a first secondary air duct 195 a and a second secondaryair duct 195 b. Moreover, each of the secondary air ducts surround anddefine a secondary air passageway. The secondary air passageways may beutilized in combination with the pulse back cleaning described herein todraw contaminants dislodged from the upstream side of the filterstructures 200 into the secondary air passageways and into a secondaryair circuit where the dislodged contaminants are discharged to anexterior area. The transverse coupling bar 193 and/or the coupling plate194 may also optionally define a portion of a clear air intake opening.

Each of the guide structures 190 is coupled to two of the secondary airducts 195 a-f such that when a second filter structure 200 is insertedthereon, the second end plate opening 277 of the second filter structure200 will be aligned with a clean air passageway formed between the twoof secondary air ducts 195 a-f. Moreover, upstream faces of each of thefilter structures 200 will be in flow communication with at last one ofthe secondary air passageways of the secondary air ducts 195 a-f toenable contaminants removed therefrom during pulse back cleaning to bedrawn into the secondary air passageway.

In FIG. 15 through FIG. 17 various pieces of a gas filtering housing areshown exploded away from one another and surrounding the bank 1200. Thegas filtering housing includes a permeable intake piece 197 e fordrawing in unfiltered air (indicated generally by arrow A in FIG. 17)and an opposite clean air outtake piece 197 f for interfacing with theclean air passageways to deliver clean filtered air downstream to a gasturbine. The gas filtering housing also includes non-permeable sidepieces 197 c and 197 d and non-permeable top and bottom pieces 197 a and197 b. The gas filtering housing is shown in phantom in FIG. 16 and FIG.17 to enable a better understanding of the interface between the bank1200 of second filter structures 200 and the other aspects of the gasfiltering system.

In some embodiments, aspects of the frame structure of the filterstructures 100 and 200 described herein may comprise pre-galvanized mildsteel with a powder coating of approximately 40 micron or greater andmaterial thickness of 1 mm or greater.

While several inventive embodiments have been described and illustratedherein, those of ordinary skill in the art will readily envision avariety of other means and/or structures for performing the functionand/or obtaining the results and/or one or more of the advantagesdescribed herein, and each of such variations and/or modifications isdeemed to be within the scope of the inventive embodiments describedherein. More generally, those skilled in the art will readily appreciatethat all parameters, dimensions, materials, and configurations describedherein are meant to be exemplary and that the actual parameters,dimensions, materials, and/or configurations will depend upon thespecific application or applications for which the inventive teachingsis/are used. Those skilled in the art will recognize, or be able toascertain using no more than routine experimentation, many equivalentsto the specific inventive embodiments described herein. It is,therefore, to be understood that the foregoing embodiments are presentedby way of example only and that, within the scope of the appended claimsand equivalents thereto, inventive embodiments may be practicedotherwise than as specifically described and claimed. Inventiveembodiments of the present disclosure are directed to each individualfeature, system, article, material, kit, and/or method described herein.In addition, any combination of two or more such features, systems,articles, materials, kits, and/or methods, if such features, systems,articles, materials, kits, and/or methods are not mutually inconsistent,is included within the inventive scope of the present disclosure.

All definitions, as defined and used herein, should be understood tocontrol over dictionary definitions, definitions in documentsincorporated by reference, and/or ordinary meanings of the definedterms.

The indefinite articles “a” and “an,” as used herein in thespecification and in the claims, unless clearly indicated to thecontrary, should be understood to mean “at least one.”

The phrase “and/or,” as used herein in the specification and in theclaims, should be understood to mean “either or both” of the elements soconjoined, i.e., elements that are conjunctively present in some casesand disjunctively present in other cases. Multiple elements listed with“and/or” should be construed in the same fashion, i.e., “one or more” ofthe elements so conjoined. Other elements may optionally be presentother than the elements specifically identified by the “and/or” clause,whether related or unrelated to those elements specifically identified.Thus, as a non-limiting example, a reference to “A and/or B”, when usedin conjunction with open-ended language such as “comprising” can refer,in one embodiment, to A only (optionally including elements other thanB); in another embodiment, to B only (optionally including elementsother than A); in yet another embodiment, to both A and B (optionallyincluding other elements); etc.

As used herein in the specification and in the claims, “or” should beunderstood to have the same meaning as “and/or” as defined above. Forexample, when separating items in a list, “or” or “and/or” shall beinterpreted as being inclusive, i.e., the inclusion of at least one, butalso including more than one, of a number or list of elements, and,optionally, additional unlisted items. Only terms clearly indicated tothe contrary, such as “only one of” or “exactly one of,” or, when usedin the claims, “consisting of,” will refer to the inclusion of exactlyone element of a number or list of elements. In general, the term “or”as used herein shall only be interpreted as indicating exclusivealternatives (i.e. “one or the other but not both”) when preceded byterms of exclusivity, such as “either,” “one of,” “only one of,” or“exactly one of.” “Consisting essentially of,” when used in the claims,shall have its ordinary meaning as used in the field of patent law.

As used herein in the specification and in the claims, the phrase “atleast one,” in reference to a list of one or more elements, should beunderstood to mean at least one element selected from any one or more ofthe elements in the list of elements, but not necessarily including atleast one of each and every element specifically listed within the listof elements and not excluding any combinations of elements in the listof elements. This definition also allows that elements may optionally bepresent other than the elements specifically identified within the listof elements to which the phrase “at least one” refers, whether relatedor unrelated to those elements specifically identified. Thus, as anon-limiting example, “at least one of A and B” (or, equivalently, “atleast one of A or B,” or, equivalently “at least one of A and/or B”) canrefer, in one embodiment, to at least one, optionally including morethan one, A, with no B present (and optionally including elements otherthan B); in another embodiment, to at least one, optionally includingmore than one, B, with no A present (and optionally including elementsother than A); in yet another embodiment, to at least one, optionallyincluding more than one, A, and at least one, optionally including morethan one, B (and optionally including other elements); etc.

It should also be understood that, unless clearly indicated to thecontrary, in any methods claimed herein that include more than one stepor act, the order of the steps or acts of the method is not necessarilylimited to the order in which the steps or acts of the method arerecited.

In the claims, as well as in the specification above, all transitionalphrases such as “comprising,” “including,” “carrying,” “having,”“containing,” “involving,” “holding,” “composed of,” and the like are tobe understood to be open-ended, i.e., to mean including but not limitedto. Only the transitional phrases “consisting of” and “consistingessentially of” shall be closed or semi-closed transitional phrases,respectively, as set forth in the United States Patent Office Manual ofPatent Examining Procedures, Section 2111.03.

1. A filter structure for removing contaminants from a stream of fluid,comprising: a front filter portion having a front frame supporting afront first filter and a front second filter; said front first filterand said front second filter in substantially parallel spaced relationto one another and defining a substantially parallel front clean airpassageway therebetween, said front frame including a front end plateextending between said front first filter and said front second filterproximal a first filter first end of said front first filter and asecond filter first end of said front second filter; a rear filterportion having a rear frame supporting a rear first filter and a rearsecond filter, said rear first filter extending from adjacent a firstfilter second end of said front first filter, said rear second filterextending from adjacent a second filter second end of said front secondfilter; said rear first filter and said rear second filter in divergingspaced relation with one another as they extend from adjacent respectiveof said front first filter and said front second filter and defining asubstantially diverging rear clean air passageway therebetween; whereinsaid rear clean air passageway and said front clean air passageway arein flow communication with one another; said rear frame including a rearend plate having a rear end plate opening in flow communication withsaid rear clean air passageway; wherein said rear end plate isconfigured for interfacing with a clean air intake opening.
 2. Thefilter structure of claim 1, wherein said front frame and said rearframe contain at least some unified structure.
 3. The filter structureof claim 2, wherein said front first filter and said rear first filtercontain at least some unified structure.
 4. The filter structure ofclaim 1, wherein said front filter portion and said rear filter portionare separable from one another.
 5. The filter structure of claim 4,wherein said front frame portion includes a second front end plateextending between said first filter second end and said second filtersecond end, said second front end plate including a second front endplate opening therein in flow communication with said front clean airpassageway, wherein said second front end plate is configured toremovably engage said rear frame.
 6. The filter structure of claim 1,wherein said front frame includes a front upper frame structure and afront lower frame structure sandwiching said front first filter and saidfront second filter.
 7. The filter structure of claim 1, wherein saidfront first filter and said front second filter share a substantiallysimilar first material configuration and said rear first filter and saidrear second filter share a substantially similar second materialconfiguration distinct from said first material configuration.
 8. Thefilter structure of claim 7, wherein said first material configurationhas a first average pleat density and said second material configurationhas a second average pleat density, said second average pleat density atleast fifteen percent more dense than said first average pleat density.9. The filter structure of claim 1, wherein said front first filter andsaid front second filter share a substantially similar first length andsaid rear first filter and said rear second filter share a substantiallysimilar second length distinct from said first length.
 10. The filterstructure of claim 10, wherein said first length is at least fifteenpercent greater than said second length.
 11. A filter structure forremoving contaminants from a stream of fluid, comprising: a generallyrectangular front filter portion and a generally trapezoidal rear filterportion; said front filter portion including front frame structuresupporting a first front filter and a second front filter insubstantially parallel spaced relation to one another; said front framestructure, said first front filter, and said second front filtersubstantially surrounding a front clean air passageway; said rear filterportion including rear frame structure supporting a first rear filterand a second rear filter in substantially divergent spaced relation withone another; a less spaced end of said first rear filter and said secondrear filter being proximal said front filter portion and a more spacedend of said first rear filter and said second rear filter being distalsaid front filter portion; said rear frame structure, said first rearfilter, and said second rear filter substantially surrounding a rearclean air passageway; wherein said rear clean air passageway is incommunication with said front clean air passageway and in communicationwith a filter structure outlet between said first rear filter and saidsecond rear filter proximal said more spaced end of said first rearfilter and said second rear filter.
 12. (canceled)
 13. (canceled) 14.The filter structure of claim 11, wherein said front first filter andsaid front second filter share a substantially similar first materialconfiguration and said rear first filter and said rear second filtershare a substantially similar second material configuration distinctfrom said first material configuration.
 15. The filter structure ofclaim 14, wherein said first material configuration has a first averagepleat density and said second material configuration has a secondaverage pleat density, said second average pleat density at least tenpercent more dense than said first average pleat density.
 16. The filterstructure of claim 14, wherein said first material configuration has afirst average pleat density and said second material configuration has asecond average pleat density, said second average pleat density at leastten percent less dense than said first average pleat density.
 17. Thefilter structure of claim 14, wherein said first material configurationhas a first grade and said second material configuration has a secondgrade distinct from said first grade.
 18. The filter structure of claim14, wherein said front filter portion and said rear filter portion areseparable from one another.
 19. A filter structure for removingcontaminants from a stream of fluid, comprising: a front filter portiondefining a front clean air passageway therein, said front filter portionhaving a first front filter and a second front filter flanking saidfront clean air passageway, said first front filter and said secondfront filter being at a first orientation relative to one another; arear filter portion coupled to said front filter portion, said rearfilter portion defining a rear clean air passageway therein, said rearclean air passageway being in flow communication with said front cleanair passageway, said rear filter portion having a first rear filter anda second rear filter flanking said rear clean air passageway, said firstrear filter and said second rear filter being at a second orientationrelative to one another; wherein said second orientation is distinctfrom said first orientation; and wherein said front first filter andsaid front second filter share a substantially similar first averagepleat density and said rear first filter and said rear second filtershare a substantially similar second average pleat density distinct fromsaid first average pleat density.
 20. The filter structure of claim 19,wherein said second average pleat density is at least fifteen percentmore dense than said first average pleat density.
 21. The filterstructure of claim 19, wherein said second average pleat density is atleast twenty-five percent more dense than said first average pleatdensity.
 22. (canceled)
 23. (canceled)
 24. (canceled)
 25. The filterstructure of claim 19, wherein said second orientation is a divergingorientation and wherein said first rear filter and said second rearfilter are more proximal one another proximal said coupling between saidfront filter portion and said second filter portion. 26-31. (canceled)